1. Field of the Invention
The invention relates to a height-variable vertebral body implant according to the preamble of claim 1, as well as to an actuating instrument set for same.
2. Description of Related Art
From DE 43 28 062 A1 a supporting bar with laterally slide-on implant bodies is known. In order to enable a sliding-on, the implant bodies are provided with a lateral groove, with a surface structure in the form of a toothing serving to fix the surfaces of the implant bodies to one another and, in addition, to maintain the position with respect to the vertebral body or bodies.
Due to the fact that the implant bodies shown therein are pre-manufactured with various heights and can be slid onto the bar, a certain height adaptation can be effected. However, the handling of the implant is extremely difficult, and the manufacturing costs are high.
From EP 0 302 719 a U-shaped implant is known wherein openings are provided which serve to introduce bone cement. Further openings may be provided for accommodating a screw in order to secure the implant immediately in the vertebra. Carbon-fiber reinforced synthetic material is specified for the shown implant.
The implant placeholder according to EP 0 268 115 A1 comprises a cylinder jacket element with a plurality of rhomboidal reticulate recesses. A ring provided therein at the upper and lower end of the cylinder jacket element prevents an undesired excessively deep penetration of the implant into the vertebra. An additionally provided base plate serves the same purpose. The cylinder jacket element is closed and has no further openings apart from the rhomboidal openings for the introduction of bone cement, so that in this case, too, there are difficulties in the surgical handling with disadvantages in the injection of bone cement.
DE 196 15 938 A1 discloses a vertebral column supporting device for carrying out an intersomatic arthrodesis. The supporting device consists of titanium, has a plane and elongated shape with an expansion in its central area. The edges with the exception of the central area are provided with a saw tooth profile. The shape of the presented supporting device is similar to that of an open ring, with the supporting device being adaptable with respect to its diameter to various applications by means of bending up the end portions of the supporting device.
A height-variable vertebral body substitution with a sleeve and with a first counter-bearing body which is displaceable in an axial direction or a second counter-bearing, respectively, is known from DE 44 09 392 A1. For moving the counter-bearing bodies relative to each other, a threaded means is provided. A similar principle is shown in DE 44 23 257 A1.
An adjustability via a thread is also mentioned in DE 195 19 101 A1, wherein tooth-shaped recesses are provided at the ends of the sleeve portions of the vertebral body substitution, in order to realize a radial locking relative to the vertebrae. The cylindrical portions of the vertebral body substitution have a plurality of recesses in order to improve the growing through with body material. The implantation of the vertebral body substitution according to DE 195 19 101 A1, however, is extremely critical because a corresponding spreading apart of the vertebrae must be effected for this purpose. In addition, the metal mass of the known implant is too great, with the corresponding, disadvantageous post-operative consequences.
DE 195 09 317 A1 shows an implant intended for being implanted as a placeholder between vertebral bodies of the vertebral column, with two end-located plate-shaped implant parts being provided interacting with an intermediate central implant part, which is rotatably connected with the end-located plate-shaped implant part. The shown implant parts are configured as tubular sleeves or as frontal rings. Bone cement may be introduced through provided openings. These openings, however, are only then optimally suited for being charged with bone cement, when they are brought to coincide, which, however, is problematical with the chosen adjusting principle.
With respect to the adjustability, reference is also made to the document U.S. Pat. No. 5,236,460, which shows a telescopic arrangement of an implant, wherein a curing material can be introduced into the telescopic space by means of a special tool. The document EP 0 637 439 A1, on the other hand, shows an implant including a wedge gear for the height adjustment. In addition, locking teeth can in this case be pivoted out so as to claw the implant between the vertebrae after its placement.
The document U.S. Pat. No. 5,290,312 concerns a height-variable vertebral body implant having two U-shaped cages with the inner cage being embraced and guided by the outer cage. The therein shown cages, however, are fixed point-wise and only unilaterally in the vertebra via screws. Moreover, for the spreading-apart operation, a forceps or similar instrument must be used, since the implant itself does not feature any such adjustment means, so that minimally invasive surgeries are not possible.